Effect of different carbon sources on Dibenzothiophene degradation and Rhamnolipids production by Burkholderia sp. C3

Dibenzothiophene (DBT) is a sulfur-containing PAH typically used as a model chemical to study biodegradation of PAHs and bioremediation. The effects of using different carbon sources (sodium gluconate, glucose, sodium pyruvate, sodium acetate and glycerol) as a co-substrates were investigated during DBT biodegradation by Burkholderia sp. C3 with respect to (i) bacterial (Burkholderia sp. C3) growth, (ii) DBT biodegradation kinetics, (iii) secretion of the biosurfactant rhamnolipids (RLs) and (iv) RLs characterization. This is the first study showing a direct association between RLs biosynthesis and DBT biodegradation induced by different carbon sources in Burkholderia species. The results indicated that bacterial growth supported by gluconate, glucose, pyruvate and glycerol, and the maximal OD600 achieved in presence of gluconate and glycerol. Glycerol and pyruvate significantly enhanced DBT biodegradation after 7 days, while glucose inhibited DBT biodegradation. RL is a glycolipid biosurfactant extensively studied in Pseudomonas species and its potential in the bioremediation field. Glycerol can induce C3 produce at least four RLs by HPLC separation and MALDI-TOF/TOF identification. Glycerol stimulated a dual function in C3 as a RL producer and a DBT degrader. The increase of RL biosynthesis and secretion facilitated biodegradation of DBT in C3. Additionally, RLs reduced the surface tension of cultures with glycerol which increased the bioavailability of DBT for Burkholderia sp. C3 to utilize it. The direct utilization of crude glycerol for bacteria to degrade pollutants must be cost-effective and environmentally friendly.